Co-Extruded Microchannel Heat Pipes

ABSTRACT

A microchannel heat pipe formed on a substrate surface using co-extruding a primary material and a secondary material such that the primary material forms side wall portions that are spaced apart by the secondary material, and an upper wall portion is formed across the upper ends of the side walls to form a composite structure. After the primary material hardens, the secondary material is removed, whereby the hardened primary material forms a pipe body having an elongated central channel defined between opposing end openings. A working fluid is then inserted into the elongated central channel, and sealing structures are then formed over both end openings to encapsulate the working fluid.

FIELD OF THE INVENTION

This invention relates to microchannel heat pipes and devices thatinclude microchannel heat pipes, and more particularly methods forproducing microchannel heat pipes on such devices.

BACKGROUND OF THE INVENTION

Heat pipes are heat transfer devices with high effective thermalconductivities that are used to transfer heat from a high temperatureregion to a low temperature region by way of a heat transfer fluid(referred to herein as a “working fluid”), whereby a temperature at thehigh region may be stabilized or reduced.

Microchannel heat pipes are heat pipes having a closed channel with asmall (often on the order of tens of micrometers) and angled (oftentriangular) cross section, and are partially filled with a working fluid(often methanol, ethanol, water, acetone, or ammonia). One end of theheat pipe (the “evaporator” section) is placed in contact with arelatively high temperature region of a host device (e.g., an integratedcircuit or a system including both an integrated circuit and an adjacentheat sink), and the other end (the “condenser” section) is placed incontact with a relatively low temperature region of the host device. Inoperation, heat generated in the high temperature region of the hostdevice is absorbed at the high temperature end of the microchannel heatpipe, causing liquid working fluid to boil. The relatively high pressurethus generated at the high temperature end forces the resultingvaporized working fluid towards the low temperature end of the heatpipe, where the vapor condenses again to liquid working fluid, thusreleasing heat. The resulting difference between the curvature of theliquid-vapor interface at the hot and cold ends of the microchannel heatpipe results in a capillary force by which the liquid working fluidflows from the low temperature end back to the high temperature end.

Microchannel heat pipes are distinguished from conventional heat pipesin that conventional heat pipes must include a wicking structure toaffect the capillary pressure difference, while in microchannel heatpipes the capillary pressure difference is a result of the small lateraldimensions of the elongated channel (central channel). The amount offluid, cross-section size and shape, fluid properties, hot and coldtemperatures, etc., determine the amount of heat that is moved from thehigh temperature end to the low temperature end. Heat fluxes of 10,000W/cm² have been demonstrated. Wire bonded micro heat pipe arrays havebeen fabricated with thermal conductivities up to 3000 W/mK, and modelshave shown that transient specific thermal conductivities of up to 200times that of copper, and steady state thermal conductivities up to 2500times that of copper should be possible.

Integrated circuits (ICs) are an example of devices that have been shownto benefit from microchannel heat pipes. As the feature size ofintegrated circuits (ICs) decreases and transistor density increases,the heat flux of ICs increases and thermal management becomes moredifficult. This is true of conventional and high power electronic chips.Circuit performance degrades significantly as temperature increases, soeffective thermal management is important. The addition of microchannelheat pipes to ICs has been shown in laboratory settings to provideeffective thermal management.

Although the beneficial heat transfer performance of microchannel heatpipes has been demonstrated in laboratory environments, they arenonetheless not commonly used in commercial devices due to the high costof incorporating the addition of microchannel heat pipes usingconventional methods. One conventional microchannel heat pipemanufacturing technique includes etching or machining a channel in thedevice's (e.g., silicon) substrate, and then sealing the channel with asecond wafer. Another conventional microchannel heat pipe manufacturingtechnique includes sintering to generate an array of parallel wiresbetween metal sheets. Such conventional methods require significantchanges to a conventional production IC fabrication flow, and thereforegreatly increase the overall manufacturing costs of the resulting ICdevices.

What is needed is a cost-effective method for producing microchannelheat pipes that can be efficiently incorporated, for example, onto an IC(e.g., as part of the IC fabrication process, or produced on the ICafter the IC fabrication process, or fabricated on a separated substratethat is then attached to a fabricated IC). What is also needed areinexpensive microchannel heat pipes formed by the method, and devicesthat are modified to include such inexpensive microchannel heat pipes.

SUMMARY OF THE INVENTION

The present invention is directed to a microchannel heat pipe includinga pipe body formed entirely by extruded primary material that isdeposited on the surface of a substrate using an inexpensiveco-extrusion process, and then cured or otherwise hardened to provide apipe structure. Because the pipe body is formed using an inexpensiveextruded material, the microchannel heat pipe can be efficientlyincorporated, for example, onto an IC (e.g., either directly as part ofthe IC fabrication process, or produced on the IC after the ICfabrication process, or fabricated on a separated substrate that is thenattached to a fabricated IC).

According to an aspect of the present invention, the pipe body of eachmicrochannel heat pipe includes first and second elongated side wallportions that are disposed on the substrate surface and are separated byan elongated central channel (void), and an upper wall portion extendingbetween upper ends of the first and second elongated side wall portionsover the elongated central channel. That is, the elongated centralchannel is defined by inside surfaces of the first and second elongatedside wall portions, an inside surface of the upper wall portion, and anupward-facing surface portion of the substrate surface that extendsbetween said first and second elongated side portions. In addition, aworking fluid encapsulated inside the elongated central channel, e.g.,by way of end structures, that functions to transfer heat in a mannersimilar to that utilized in conventional microchannel heat pipes.

According to an embodiment of the present invention, the entire pipebody of each microchannel heat pipe (i.e., the first and secondelongated side wall portions and the upper wall portion) are composed ofa common material (i.e., the cured or otherwise hardened form of asingle extruded “primary” material) that forms an integral structure.Practical elongated pipe bodies have nominal widths in the range of 10micrometers to 500 micrometers, lengths in the range of 100 micrometersto 20 centimeters, and nominal heights in the range of 25 micrometers to500 micrometers. The common material forming the pipe body includes oneor more of silver, copper, nickel, tin, aluminum, steel, alumina,silicates, glasses, carbon black, polymers and wax. In one specificembodiment a metal included in the pipe body is sintered. By modifyingthe co-extrusion process utilizing methods described below, the pipebody is formed with a cross-sectional shape that is either substantiallysemi-circular, substantially square, substantially rectangular,pseudo-trapezoidal or pseudo-triangular. Because any of these pipe bodystructures is achievable using the novel and cost-efficient co-extrusionproduction method described below, and each pipe body construction isdistinguished over conventional trench-type and wire-type heat pipes inthat it can be entirely formed using a single co-extrusion process.

According to another aspect of the present invention, each microchannelheat pipe includes a working fluid that is encapsulated inside theelongated central channel of the pipe body. In exemplary embodiments theworking fluid includes one of methanol, ethanol, water, acetone, andammonia (or another suitable fluid) that is selected based on theworking environment in which the microchannel heat pipe will be used. Inother embodiments, encapsulation of the working fluid inside theelongated central channel is achieved by forming sealing structures overopposing end openings defined in the pipe body that communicate with theelongated central channel. In exemplary embodiments the sealingstructures include one of epoxy, silicone and solder.

According to an embodiment of the present invention, each pipe body ofeach microchannel heat pipe comprises polymer walls that are formedafter the extrusion process by activating materials provided in eitherthe primary or secondary (sacrificial) extrusion materials (or both). Anadvantage of this structure is that the fabrication process andresulting pipe body structure are compatible with conventional ICfabrication techniques.

According to an embodiment of the present invention, a host device(e.g., an IC device or system) includes multiple microchannel heat pipeformed in accordance with the features described above, where one end ofeach microchannel heat pipe is disposed over an active (heat generating)region of the host device, and the other end is positioned over aninactive (heat sink or otherwise cool) region of the host device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings, where:

FIG. 1 is a partial perspective view showing a microchannel heat pipeproduced in accordance with an embodiment of the present invention;

FIG. 2 is a simplified flow diagram indicating a generalized method forgenerating the microchannel heat pipe of FIG. 1 according to anotherembodiment of the present invention;

FIGS. 3(A), 3(B), 3(C) and 3(D) are simplified cross-sectional end viewsshowing the formation of the microchannel heat pipe of FIG. 1 accordingto the generalized method of FIG. 2;

FIGS. 4(A), 4(B), 4(C) and 4(D) are simplified cross-sectional sideviews showing the formation of the microchannel heat pipe of FIG. 1according to the generalized method of FIG. 2;

FIG. 5 is a front view showing a micro-extrusion system including ageneralized co-extrusion printhead assembly utilized during thegeneralized method of FIG. 2 in accordance with an embodiment of thepresent invention;

FIG. 6 is an exploded perspective view showing the co-extrusionprinthead assembly of FIG. 5 in additional detail;

FIG. 7 is a simplified exploded partial perspective view showing aportion of a generalized layered nozzle structure utilized in theco-extrusion printhead assembly of FIG. 6;

FIGS. 8(A) and 8(B) are partial cross-sectional views showing asimplified three-part fluidic channel defined in the co-extrusionprinthead assembly of FIG. 6 prior to and during a co-extrusion process,respectively;

FIG. 9 is a partial perspective view showing the formation ofmicrochannel heat pipes on an integrated circuit using themicro-extrusion system of FIG. 5 according to another specificembodiment of the present invention;

FIGS. 10(A), 10(B) and 10(C) are cross-sectional side views illustratingthe formation of a co-extruded pipe structure according to a firstspecific embodiment of the present invention;

FIGS. 11(A) and 11(B) are cross-sectional side views illustrating theformation of a co-extruded pipe structure according to a second specificembodiment of the present invention;

FIGS. 12(A), 12(B) and 12(C) are cross-sectional side views illustratingthe formation of a co-extruded pipe structure according to a thirdspecific embodiment of the present invention;

FIGS. 13(A) and 13(B) are cross-sectional side views illustrating theformation of a co-extruded pipe structure according to a fourth specificembodiment of the present invention;

FIGS. 14(A), 14(B) and 14(C) are cross-sectional side views illustratingthe formation of a co-extruded pipe structure according to a fifthspecific embodiment of the present invention;

FIGS. 15(A), 15(B) and 15(C) are cross-sectional side views illustratingthe formation of a co-extruded pipe structure according to a sixthspecific embodiment of the present invention;

FIGS. 16(A) and 16(B) are cross-sectional side views illustrating theremoval of secondary material from a pipe structure according to anotherspecific embodiment of the present invention;

FIG. 17 is a cross-sectional side view illustrating the removal ofsecondary material from a pipe structure according to another specificembodiment of the present invention;

FIGS. 18(A), 18(B) and 18(C) are cross-sectional side views illustratingcharging the pipe structure with working fluid according to anotherspecific embodiment of the present invention;

FIGS. 19(A), 19(B) and 19(C) are cross-sectional side views illustratingcharging the pipe structure with working fluid according to anotherspecific embodiment of the present invention; and

FIGS. 20(A) and 20(B) are cross-sectional end views showingpseudo-trapezoidal and pseudo-triangular pipe structures according toalternative specific embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention relates to an improvement in micro-extrusionsystems. The following description is presented to enable one ofordinary skill in the art to make and use the invention as provided inthe context of a particular application and its requirements. As usedherein, directional terms such as “upper”, “top”, “lower”, “bottom”,“front”, “side” and “rear” are intended to provide relative positionsfor purposes of description, and are not intended to designate anabsolute frame of reference. In addition, the phrase “integralstructure” is used herein to describe a structure including wallportions that are chemically bonded or otherwise joined without anintervening fastening material such as an adhesive or solder. Variousmodifications to the preferred embodiment will be apparent to those withskill in the art, and the general principles defined herein may beapplied to other embodiments. Therefore, the present invention is notintended to be limited to the particular embodiments shown anddescribed, but is to be accorded the widest scope consistent with theprinciples and novel features herein disclosed.

FIG. 1 is a top perspective view showing a microchannel heat pipe 100disposed on the upper surface 102 of a substrate 101 according to anexemplary embodiment of the present invention. Microchannel heat pipe100 is formed on substrate 101 utilizing the method set forth below, andgenerally includes an elongated pipe body 112 that defines, inconjunction with a surface portion 102-1 of substrate 101, an elongatedcentral channel 115 containing an amount of working fluid 130, and endseal structures 140-1 and 140-2 that are respectively disposed overopposing ends of elongated central channel 115 such that working fluid130 is encapsulated (sealed) inside elongated central channel 115.Microchannel heat pipe 100 operates in a manner consistent withconventional microchannel heat pipes in that heat from a relatively hightemperature applied at one end is absorbed in the form of vaporizedworking fluid, and is rejected the opposite (condenser) end, which ismaintained at a relatively low temperature that causes condensation ofthe vaporized working fluid.

Referring to the middle of FIG. 1, elongated pipe body 110 is anelongated structure having one of a generally semi-circular (shown),pseudo triangular (preferred) or pseudo trapezoidal cross section thatis disposed on upper surface 102. For descriptive purposes, opposingside portions of elongated pipe body 110 are respectively referred toherein as first elongated side wall portion 111 and second elongatedside wall portion 112, and the upper portion of elongated pipe body 110is referred to as upper wall portion 113. Side wall portions 111 and 112are disposed on surface 102 in a substantially parallel, spaced-apartmanner along an entire length L of elongated pipe body 112 such that allportions of side wall portion 111 are spaced from corresponding opposingportions of side wall portion 112 by an elongated central channel 115having a nominal channel width W1 (measured at upper surface 102). Upperwall portion 113 is supported by upper edges of elongated side wallportions 111 and 112 at a nominal channel height H1 (measured from uppersurface 102 to the lower surface of upper wall portion 113), and extendsalong the entire length of first and second elongated side wall portions111 and 112. Accordingly, elongated central channel 115 is defined(surrounded) by elongated side wall portions 111 and 112, upper wallportion 113, and a portion 102-1 of substrate surface 102 that extendingbetween elongated side wall portions 111 and 112. Elongated centralchannel 115 extends the entire length L of pipe body 112 (i.e., betweena first end opening 116 and a second end opening 117), and has asubstantially constant cross-sectional area.

With reference to microchannel heat pipe 110 of FIG. 1, the phrase“microchannel heat pipe” is defined herein to heat pipe structuresincluding a single elongated central channel having a nominal width W1in the range of 10 micrometers to 500 micrometers, a length L in therange of 100 micrometers to 20 centimeters, and a nominal height H1 inthe range of 25 micrometers to 500 micrometers. Optimal dimensions ofmicrochannel heat pipe 110 are determined in each instance by, forexample, the properties of the working fluid and working temperatures.In a typical exemplary embodiment, microchannel heat pipe 110 has awidth dimension W1 in the range of 30-200 micrometers, a height H1 inthe range of 30-200 micrometers, and a length dimension L in the rangeof 10-100 millimeters.

According to another aspect of the present invention, elongated pipebody 110 comprises one or more cured or otherwise hardened extrudedmaterials having sufficient strength to withstand the internal pressuresgenerated by working fluid 130. In one embodiment, the entirety of pipebody 110 (i.e., side wall portions 111 and 112 and upper wall portion113) comprises an integral structure formed by a single (common)extruded material (i.e., the entire pipe body structure is formed fromintegrally connected wall portions having the same chemical compositionthat are generated during a single co-extrusion process involving asingle primary material, and then subjected to a post-extrusion curing,sintering, polymerizing or other hardening process). In anotherembodiment, an integral structure is formed by side wall portions 111and 112 of pipe body 110 are formed by a two extruded materials, andupper wall portion 113 is formed by a second extruded primary material,where both the first and second primary materials are subjected to ahardening process. As set forth below, in exemplary embodiments thecured or otherwise hardened material(s) of pipe body 110 includes one ofsilver, copper, nickel, tin, aluminum, steel, alumina, silicates,glasses, carbon black, polymers and wax, although the use of anink/paste including a metal powder or ceramic in a solvent may require apost-processing step (e.g., sintering) to produce a fully dense shell.In one specific embodiment set forth below, the side and upper walls ofpipe body 110 are polymer or wax. Such polymer (or wax) pipe bodies arepresently preferred because they do not require a densifying step (e.g.,sintering). Those skilled in the art will recognize that elongated pipebody structures may be formed using materials other than the exemplarymaterials mentioned herein.

Referring again to FIG. 1, working fluid 130 is disposed insideelongated central channel 115, and in exemplary embodiments consists ofeither methanol, ethanol, water, acetone, or ammonia. Other workingfluids may also be utilized based on various parameters such as boilingpoint, partial pressure at different temperatures, the dimensions of theheat pipe, and the working temperatures. The amount of working fluid 130disposed inside microchannel heat pipe 100 is determined by the volumeof elongated central channel 115, and in an exemplary embodiment theamount may be approximately 50% of this channel volume, although theamount may be selected to fill 1% to 99% of the void (i.e., the channelvolume).

End seal structures 140-1 and 140-2 are respectively formed using asealant material that can withstand the temperatures to whichmicrochannel heat pipe 100 will be exposed, and the pressure of theworking fluid vapor during operation. Currently preferred sealantsinclude epoxy and silicone, but solder or another metal can also beused.

FIG. 2 is a flow diagram showing a simplified method for producingexemplary microchannel heat pipe 100 (see FIG. 1) in accordance withanother embodiment of the present invention. Referring to the upper endof FIG. 2, the method begins by providing a suitable substrate uponwhich the microchannel heat pipe will be formed (block 205), forming theheat pipe structure on the substrate by co-extruding two materials(block 210), removing one of the materials to form an elongated centralchannel extending entirely through the heat pipe structure (block 220),charging the heat pipe structure with an amount of working fluid (block230), and sealing the ends of the heat pipe to encapsulate the workingfluid (block 240). Each of these method portions are described below inadditional detail.

As indicated by block 205 at the top of FIG. 2, the process begins withthe optional step of preparing the upper surface of a suitable substratefor production of a microchannel heat pipe, and may involve chemicallytreating the upper surface to produce suitable adherence between thesubsequently extruded primary materials and the substrate. In oneexemplary embodiment described below with reference to FIG. 9, themicrochannel heat pipe production process is performed after thefabrication of an integrated circuit on a suitable semiconductorsubstrate (e.g., monocrystalline silicon), which the IC fabrication isperformed, for example, using a known semiconductor (e.g., CMOS)fabrication technique. In other embodiments the microchannel heat pipesof the present invention are formed on “plain” (e.g., metal foil)substrates that are then transferred onto a host device. This optionalstep may be omitted when the process is utilized to form microchannelheat pipes on substrates or host devices that do not requirepre-treatment.

FIGS. 3(A) to 3(D) and 4(A) to 4(D) depict the processes performed byblocks 210 to 240 of FIG. 2 in additional detail.

FIGS. 3(A) and 4(A) are simplified illustrations depicting the formationof an elongated composite structure 110-1 using a co-extrusion processin which a first material 56 and a second material 57 are simultaneouslyextruded onto a surface 102 of the substrate in accordance with block210 of FIG. 2. As set forth in additional detail below, the co-extrusionprocess is carried out such that primary material 56 and secondarymaterial 57 form an elongated composite structure 110-1. As indicated inFIG. 3(A), primary material 56 forms a first elongated side portion111-1 and a second elongated side portion 112-1, and secondary material57 forms an elongated bead 114 that entirely fills an elongated centralregion 115-1 disposed between first and second elongated side portions111-1 and 112-1. As indicated in FIG. 4(A), side portions 111-1 and112-1 and bead 114 extend the entire length of elongated structure 110-1between a first end 116-1 and a second end 117-1. As described inadditional detail below, a benefit of co-extruding primary material 56and secondary material 57 in this manner is that, by controlling theextrusion process parameters and by selecting primary and secondarymaterials that do not intermix, first and second elongated side portions111-1 and 112-1 are reliably produced at a predetermined sub-millimeterspacing (width W1) that is maintained by the presence of bead 114 untilfirst and second elongated side portions 111-1 and 112-1 are cured orotherwise harden to form side walls of the desired pipe structure.Another benefit of the depicted co-extrusion process is that bead 114 isretained between side portions 111-1 and 112-1, thereby facilitating theuse of secondary material 57 in a liquid form that facilitates easyremoval.

Referring to the upper portion of FIG. 3(A), according to another aspectof the present invention, an upper portion 113-1 of elongated structure110-1 is either simultaneously or subsequently deposited or otherwiseformed over bead 114 in accordance with the various specific embodimentsdescribed below. Upper portion 113-1 can either be composed of primarymaterial 56 or a third material that is compatible with primary material56 such that a coherent pipe structure is produced after thecuring/hardening process that is capable of encapsulating a workingfluid. As indicated in FIG. 4(A), which shows upper portion 113-1 afterdeposition/formation, a benefit of forming upper portion 113-1 on bead114 in this manner is that upper wall portion 113-1 is maintained at thedesired spacing (height H1) by the presence of bead 114 until upperportion 113-1 is cured or otherwise harden to form an upper wall of thedesired pipe structure.

As mentioned above, once the formation of elongated composite structure110-1 is completed (i.e., with upper portion 113-1 disposed on bead 114,as indicated in FIG. 4(B), an optional curing process is performed (ifneeded) such that side portions 111-1 and 112-1 and upper portion 113-1harden (or are utilized to produce) a rigid pipe structure. Fordescriptive purposes, the transition of the liquid or semi-liquidextruded structures that form the outer surface of elongated compositestructure 110-1 to the solid, shell-like, pipe structure utilized in thefinal microchannel heat pipe structure is indicated herein by a changeof the suffix “−1” to the suffix “2”. That is, after curing/hardening iscomplete, elongated composite structure 110-1 becomes pipe body 110-2,with liquid/semi-liquid side portion 111-1 of elongated compositestructure 110-1 being hardened to become side wall 111-2 of pipe body110-2, side portion 112-1 being hardened to become side wall 112-2 ofpipe body 110-2, and upper portion 113-1 becoming upper wall 113-2 ofpipe body 110-2. Note that the hardening process may not involve aseparate process step, and instead may occur immediately upon depositionof elongated composite structure 110-1 onto the target substrate. Notealso that the transition of side portions 111-1 and 112-1 and upperportion 113-1 to side wall portions 111-2 and 112-2 and upper wall 113-2may involve a chemical change to one or more of the co-extrudedmaterials (e.g., the formation of a polymer structure, as describedbelow with reference to FIGS. 12 and 13).

FIGS. 3(B) and 4(B) show pipe body 110-2 after the curing/hardeningprocess is completed, and also depict the subsequent process of removingsecondary material from the elongated central region of the co-extrudedcomposite structure according to block 220 of FIG. 2. In particular,these figures show the result of the secondary material removal process,which is to define an elongated central channel 115-2 through pipestructure 110-2 that has substantially the same width W1 and height H1of the removed secondary material bead. That is, as indicated in FIG.3(B), elongated central channel 115-2 is defined by spaced-apart firstand second side wall portions 111-2 and 112-2 and upper wall portion113-2 of pipe body 110-2, and by surface portion 102-2, an as indicatedin FIG. 4(B), elongated central channel 115-2 extends the entire lengthof rigid pipe body 110-2 between a first end opening 116-2 and a secondend opening 117-2 of pipe body 110-2. As indicated in FIG. 4(B), theremoval of secondary material 57 generally involves transportingsecondary material 57 through one or both of end openings 116-2 and117-2, and exemplary removal processes are described below withreference to FIGS. 16 and 17.

FIGS. 3(C) and 4(C) show pipe body 110-2 after the curing/hardeningprocess is completed, and also depict the subsequent process of chargingpipe body 110-2 with an amount of working fluid according to block 230of FIG. 2. In particular, these figures show the result of disposing anamount of working fluid 130 inside elongated central channel 115-2. Asindicated in FIG. 4(B), the disposition of working fluid 130 intoelongated central channel 115-2 generally involves injecting or drawingworking fluid 130 through one or both of end openings 116-2 and 117-2,and exemplary charging processes are described below with reference toFIGS. 18 and 19. In alternative embodiments, the amount of working fluid130 disposed in central channel 115-2 is either apredetermined/premeasured amount that is injected into central channel115-2, or determined using a sensor (e.g., a pressure sensor) or anothermeasuring mechanism during an evaporation portion of the chargingprocess.

FIGS. 3(D) and 4(D) show the final process step in which sealingstructures are mounted over end openings 116-2 and 117-2 of pipe body110-2 to complete the production of microchannel heat pipe 100 accordingto block 240 of FIG. 2. In particular, these figures show the result ofdisposing a first sealing structure 140-1 over end opening 116-2 and asecond sealing structure 140-2 over end opening 117-2, thereby enclosingelongated central channel 115-2 to encapsulate working fluid 130therein. Exemplary sealing charging are described below with referenceto FIGS. 18 and 19.

FIGS. 5-7 illustrate a co-extrusion system 50 utilized to produce themicrochannel heat pipes of the present invention according an embodimentof the present invention. As set forth below, co-extrusion system 50 ischaracterized by using one extruded material (i.e., fluid or paste) tofocus or concentrate the flow of another extruded fluid/paste, therebyfacilitating the creation of fine, high aspect ratio structures fromprint nozzles that are significantly wider than the high aspect ratiostructures. However, unlike previous uses of co-extrusion system 50,where the high aspect ratio structures are retained in the finalproduct, the novel process described herein includes removing theextruded high aspect ratio structures to define the elongated centralchannel of a pipe structure.

Referring to FIG. 5, system 50 generally includes a material feedmechanism 60 that supplies two extrusion materials to a co-extrusionprinthead assembly 90, and an X-Y-Z axis positioning mechanism (notshown) that is used to move co-extrusion printhead assembly 90 over atarget device (not shown). Material feed mechanism 60 supplies the twoextrusion materials to co-extrusion printhead assembly 90 in response tocontrol signals from a controller (not shown), and printhead assembly 90is constructed to co-extrude the two extrusion materials in a mannerthat generates parallel high-aspect ratio structures (described below,e.g., with reference to FIG. 9). Referring to the upper portion of FIG.5, material feed mechanism 60 includes a pair of housings 62-1 and 62-2that respectively support pneumatic cylinders 64-1 and 64-2, which isoperably coupled to cartridges 66-1 and 66-2 such that material forcedfrom these cartridges respectively passes through feedpipes 68-1 and68-2 into printhead assembly 90. As indicated in the lower portion ofFIG. 5, the X-Y-Z axis positioning mechanism (partially shown) includesa Z-axis stage 72 that is movable in the Z-axis (vertical) direction byway of a housing/actuator 74 (partially shown) using known techniques.Mounting plate 76 is rigidly connected to a lower end of Z-axis stage 72and supports printhead assembly 90, and a mounting frame (not shown) isrigidly connected to and extends upward from Z-axis stage 72 andsupports pneumatic cylinders 64-1 and 64-2 and cartridges 66-1 and 66-2.

FIG. 6 is an exploded perspective view showing micro-extrusion printhead90 in additional detail. Micro-extrusion printhead 90 generally includesa first (back) plate structure 91, a second (front) plate structure 93,and a layered nozzle structure 95 connected therebetween. Back platestructure 91 and front plate structure 93 serve to guide primaryextrusion material 56 and secondary extrusion material 57 fromcorresponding inlet ports 96-1 and 96-2 to layered nozzle structure 95,and to rigidly support layered nozzle structure 95 such that extrusionnozzles defined in layered nozzle structure 95 are pointed toward thetarget substrate at a predetermined tilted angle (e.g., 45°), wherebyextruded material traveling down each extrusion nozzle toward itscorresponding nozzle orifice 99 is directed toward the target substrate.

Referring to the upper portion of FIG. 6, back plate structure 91includes a molded or machined metal (e.g., aluminum) angled back plate91-1, a back plenum 91-2, and a back gasket 91-3 disposed therebetween.Angled back plate 91-1 includes front and back surfaces that form apredetermined angle θ2 (e.g., 45°) that facilitates proper positioningof printhead 90 over a target device (substrate). Angled back plate 91also defines a pair of bores (not shown) that respectively extend fromthreaded countersunk bore inlets 92-1 and 92-2 to corresponding conduitsdefined through back plenum 91-2 and a back gasket 91-3. Thebores/conduits defined through back plate structure 91 feed extrusionmaterials 56 and 67 to layered nozzle structure 95 in the mannerindicated by the dashed-line arrows.

Referring to the lower portion of FIG. 6, front plate structure 93includes a molded or machined metal (e.g., aluminum) front plate 93-1, afront plenum 93-2, and a front gasket 93-3 disposed therebetween. Frontplate 93-1 includes surfaces that form the predetermined angle describedabove, and defines several holes for attaching to other sections ofprinthead assembly 90, but does not channel extrusion material. Frontplenum 93-2 includes parallel front and back surfaces, and defines aconduit (not shown) extending from a corresponding inlet to acorresponding outlet to support the flow of primary material 56 asindicated by the dashed-line arrows.

Layered nozzle structure 95 includes a top nozzle plate 95-1, a bottomnozzle plate 95-2, and a nozzle outlet plate 95-3 sandwiched between topnozzle plate 95-1 and bottom nozzle plate 95-2. As described inadditional detail below, top nozzle plate 95-1 defines a row ofsubstantially circular inlet ports (through holes) 96-11 and acorresponding series of elongated inlet ports 96-12 that are alignedadjacent to a front edge 95-11. Bottom nozzle plate 95-2 is asubstantially solid (i.e., continuous) plate having a front edge 95-21,and defines several through holes 96-2, whose purposes are describedbelow. Nozzle outlet plate 95-3 includes a front edge 95-31, and definesa row of three-part nozzle channels 97 that are described in additionaldetail below, and several through holes 96-3 that are aligned withthrough holes 96-2. When operably assembled, nozzle outlet plate 95-3 issandwiched between top nozzle plate 95-1 and bottom nozzle plate 95-2 toform a series of nozzles in which each three-part nozzle channel 97 isenclosed by corresponding portions of top nozzle plate 95-1 and bottomnozzle plate 95-2 in the manner described above, with each part ofthree-part nozzle channel 97 aligned to receive material from two inletports 96-11 and one elongated inlet port 96-12. As described inadditional detail below, this arrangement produces parallel high-aspectratio structures in which secondary material 57 is pressed between twoelongated side portions formed by primary material 56.

In addition to top nozzle plate 95-1, bottom nozzle plate 95-2 andnozzle outlet plate 95-3, layered nozzle structure 95 also includes afirst feed layer plate 95-4 and a second feed layer plate 95-5 that arestacked over top nozzle plate 95-1 and serve to facilitate the transferof the two extrusion materials to nozzle outlet plate 95-3 in thedesired manner described below. First feed layer plate 95-4 is asubstantially solid (i.e., continuous) plate having a front edge 95-41,and defines several Y-shaped through holes 96-4 located adjacent tofront edge 95-51, and several additional holes for feeding material andfor assembly. Second feed layer plate 95-5 is disposed immediately belowfirst feel layer plate 95-4, includes a front edge 95-51, and definesseveral substantially circular through holes 96-5 located adjacent tofront edge 95-51, and several feed and assembly holes.

As indicated by the dashed arrows in FIG. 6 and described in additionaldetail in FIG. 7, primary extrusion material 56 and secondary extrusionmaterial 57 are fed by way of two separate paths in a substantiallyZ-axis direction through the various layers of layered nozzle structure95 to nozzle outlet plate 95-3. The two flow paths are described indetail in the following paragraphs.

Referring to the upper portion of FIG. 6, secondary material 57 injectedthrough inlet port 92-1 is fed downward through back plenum 91-2 andpasses through aligned openings respectively formed in first feed layerplate 95-4, second feed layer plate 95-5, top nozzle plate 95-1, nozzleoutlet plate 95-3, and bottom nozzle plate 95-2 before entering opening94-21 of front plenum 93-2. As indicated in FIG. 6 and in additionaldetail in FIG. 7, secondary material 57 is then redirected by frontplenum 93-2 and moves upward from opening 94-22 through opening 96-2formed in bottom nozzle plate 95-2 and opening 96-3 formed in nozzleoutlet plate 95-3. As indicated in the upper portion of FIG. 7,secondary material 57 then enters the rearward end of elongated openings96-12, and is redirected in a substantially horizontal direction alongthe path indicated by arrow F1A to the front end of elongated opening96-12. Secondary material 57 is then forced downward into a centralchannel 98-12 of three-part nozzle channel 97, then flows along centralchannel 98-12 in the direction of arrow F1 into a merge point 98-13 andonward toward dispensing orifice 99. In the manner described above, eachcentral channel 98-12 communicates with inlet port 92-1 to passsecondary material 57 to an associated dispensing orifice 99. Asexplained in additional detail below, under selected operatingconditions, the secondary material flowing along each central channel98-12 in the direction of arrow F1 is compressed between correspondingprimary material portions in merge point 98-13 before exiting fromassociated dispensing orifice 99.

Referring again to the upper portion of FIG. 6, primary material 56injected through inlet port 92-2 is fed downward through back plenum91-2, where it is dispersed and is passed into the rearward end ofY-shaped elongated channels 96-4, which are formed in first feed layerplate 95-4. As indicated by dashed arrows in FIG. 7, primary material 56flows along each Y-shaped elongated channel 96-4 to a split front endregion, where the primary material is distributed through correspondingopenings 96-5 disposed in second feed layer plate 95-5 and openings96-11 disposed in top nozzle plate 95-1, and then into opposing sidechannel 98-11 of three-part nozzle channel 97. As described inadditional detail below, the primary material then flows along sidechannels 98-11, and at merge region 98-13 presses against thecorresponding secondary material flowing from channel 98-11, therebycreating a two part flow 55 (made up of primary and secondary material)that then exits from orifice 99. Techniques for fabricating theprinthead described above are described, for example, in co-owned U.S.Pat. No. 7,780,812, entitled “EXTRUSION HEAD WITH PLANARIZED EDGESURFACE”, which is incorporated herein by reference in its entirety.

FIG. 8(A) is a simplified partial section view showing a portion ofnozzle output plate 95-2, which in the exemplary embodiment includes ametal plate that is micro-machined (e.g., using deep reactive ionetching) to include arrowhead-shaped three-part nozzle channel 97including a central channel 98-12 and opposing (first and second) sidechannels 98-11. Central channel 98-12 is separated from each sidechannel 98-11 by an associated tapered finger of plate material. Centralchannel 98-12 has a closed end that is aligned to receive secondarymaterial from the front end of elongated opening 96-12 by way of the topnozzle plate, and an open end that communicates with merge point 98-13.Similarly, side channels 98-11 have associated closed ends that arealigned to receive primary material from corresponding openings 96-11 byway of the top nozzle plate, and open ends that communicate with mergepoint 98-13. Side channels 98-11 are angled toward central channel 98-12such that primary material is directed toward opposing sides of thesecondary material flowing from central channel 98-12 toward orifice 99.

FIG. 8(B) shows the portion of nozzle output plate 95-2 (described abovewith reference to FIG. 8(A)) while primary and secondary materials aresimultaneously co-extruded (forced) through co-extrusion printheadassembly 90 and out of nozzle outlet orifice 99, and also shows across-sectional end view of an exemplary elongated body structure 110-1formed as a result of the co-extrusion process. A benefit of theco-extrusion approach described herein is that elongated body structure110-1 includes a high-aspect ratio bead structure 114 in which secondarymaterial is supported by primary material side portions 111-1 and 112-1,which are respectively disposed on opposing sides of bead structure 114.The shape of extruded structures (i.e., the aspect ratio of the centralbead structure 114 and the shape of the primary side portions 111-1 and111-2) are controllable through at least one of the shapes of the one ormore outlet orifice 99, the internal geometry of printhead assembly 90,characteristics of the materials (e.g., viscosity, etc.), and theextrusion technique (e.g., flow rate, respective pressures P21 and P22respectively applied to the secondary and primary materials,temperature, etc.). The structure within the printhead assembly and theshape of the nozzle outlet orifices may be modified to further enhancethe extrusion process in order to generate the desired pipe shape.

Suitable primary materials include, but are not limited to, silver,copper, nickel, tin, aluminum, steel, alumina, silicates, glasses,carbon black, polymers and waxes, and suitable secondary (sacrificial)materials include plastic, oil, cellulose, latex,polymethylmethacrylate, etc., combinations thereof, and/or variationsthereof, including combining the above with other substances to obtain adesired density, viscosity, texture, color, etc. In one embodiment, anink/paste including a metal powder or a ceramic in a solvent is used asthe extruded primary material, and then sintering is performed tosolidify (densify) the pipe body structure. Alternatively, themetal/ceramic-based primary material is utilized to form the pipe body,and a sealing process is subsequently performed in which the entire pipebody structure (including the end openings) is covered with an epoxyafter working fluid is disposed inside the central chamber.

FIG. 9 is a simplified partial perspective view illustrating a portionof system 50 and an IC (host device) 300 including a semiconductor(e.g., silicon) substrate 101A, and in particular depicts thesimultaneous formation of multiple elongated composite structures 110-1on an upper surface 102A of substrate 101A using system 50 according toanother embodiment of the present invention. As set forth above, system50 generally includes a controller 51 that controls material feedmechanisms 60-1 and 60-2 and an X-Y-Z-axis positioning mechanism 70 toselectively force primary material 56 and secondary material 57 fromprinthead assembly 90 onto upper surface 102A of substrate 101A asdescribed above in order to form multiple parallel elongated compositestructures 110-1. Controller 51 (e.g., a microprocessor and associatedsoftware) is programmed according to known techniques to generate andtransmit control signals to material feed mechanisms 60-1 and 60-2 andX-Y-Z-axis positioning mechanism 70 in accordance with the productionmethods. Material feed mechanism 60-1 includes an actuator 62-1 that isoperably disposed to supply a pressure P21 to a secondary materialsource 65-1, whereby secondary material 57 is forced from materialsource 65-1 through inlet ports 92-1 into printhead assembly 90.Similarly, material feed mechanism 60-2 includes an actuator 62-2 thatis operably disposed to supply a pressure P22 to a primary materialsource 65-2, whereby primary material 56 is forced from material source65-2 through inlet ports 92-2 into printhead assembly 90. X-Y-Z-axispositioning mechanism 70 generally includes mounting plate 76 forrigidly supporting and positioning printhead assembly 90 relative tosubstrate 101A, a base (not shown) for supporting substrate 101, and oneor more motors, associated positioning structures (not shown) andcontrol circuitry that facilitate relative movement of printheadassembly 90 relative to substrate 101A in response to control signalsreceived from controller 51. Suitable X-Y-Z positioning mechanisms arewell known to those skilled in the art. Utilizing this approach, asindicated in FIG. 9, multiple elongated composite structures 110-1 areformed on substrate 101A, with a second portion of each structure 110-1disposed over a central “active” (heat generating) region 303 of IC 300(i.e., CMOS circuitry that is disposed in substrate 101A), and a secondportion of each structure 110-1 disposed over a peripheral “inactive”region (or heat sink structure) 304, which is also provided on substrate101A and spaced from “active” region 303 of IC 300. By completing theproduction method described herein, each of these elongated compositestructures 110-1 can be formed into a microchannel heat pipe of thepresent invention that is disposed to transfer heat from active (hot)central region 303 of IC 300 to peripheral inactive (cool) region 304 ofIC 300. Note that FIG. 9 is provided for descriptive purposes, and thedepicted structures are not necessarily to scale. In other embodiments,microchannel heat pipes 100 may be formed on a bare metal,semiconductor, ceramic, or other substrate that is then attached, forexample, to the upper or lower surface of an IC device or other hostdevice. Other host devices to which micro-channel heat pipes 100 may beattached include an LED, a laser diode, or other solid state device thatgenerates hear, a thermoelectric device or other device that providesactive cooling, a heat sink, or other device that provides passivecooling.

FIGS. 10(A) to 15(C) depict several specific embodiments for formingelongated composite structures utilizing the co-extrusion processdescribed above.

FIGS. 10(A) to 10(C) depict a first specific embodiment involving atwo-part process that is utilized to produce elongated compositestructures. FIG. 10(A) depicts a first part of the two-part process, andinvolves co-extruding a primary material 56A-1 and a secondary material57A in the manner described above to produce a preliminary compositestructure including side structures 111A-1 and 112A-1 and a central bead114A disposed therebetween. Note that the preliminary compositestructure shown in FIG. 10(A) is formed such that an upper surface ofcentral bead 114A is exposed (i.e., not covered by primary material).FIG. 10(B) depicts composite structure 110A-1 after a second part of thetwo-part process in which a third material 56A-2 (which is eitheridentical to primary material 56A-1 or suitably compatible) is extrudedor printed onto the preliminary composite structure, whereby the thirdmaterial forms an elongated upper portion 113A-1 that extends betweenupper edges of elongated side portions 111A-1 and 112A-1 such that acentral portion of upper wall 113A-1 is supported by bead 114A (i.e., bysecondary material 57A). FIG. 10(C) depicts a resulting pipe structure110A-2 after subsequent curing/hardening of the primary and thirdmaterials to form side walls 111A-2 and 112A-2 and upper wall 113A-2,and the removal of the secondary material to form central channel115A-2, which is defined by inside surfaces of walls 111A-2, 112A-2 and113A-2 and exposed substrate surface portion 102-2. An advantage of thisfirst approach is that coextruding materials side-by-side can simplifythe printhead, although this approach requires two extrusion steps.

FIGS. 11(A) and 11(B) depict a second specific embodiment in which theco-extrusion process is performed using a modified co-extrusionprinthead including a fourth nozzle inlet to the material merge pointsuch that primary material 56B is simultaneously extruded onto the uppersurface of secondary material 57B, which forms central bead 114B,whereby side portions 111B-1 and 112B-1 and an upper portion 113B-1 areformed during a single co-extrusion pass. Suitable printheadmodifications capable of generating such vertical layering aredescribed, for example, in co-owned U.S. Pat. No. 7,765,949, which isincorporated herein by reference in its entirety. FIG. 11(A) depictscomposite structure 110B-1 formed by this method immediately after theco-extrusion process, and FIG. 11(B) depicts a resulting pipe structure110B-2 after subsequent curing/hardening of the primary material to formside walls 111B-2 and 112B-2 and an upper wall 113B-2, and the removalof the secondary material to form central channel 115B-2 (which isbounded at its lower end by substrate surface portion 102-2. Anadvantage of this second approach is that the heat pipe can be formedwith a single extrusion step.

FIGS. 12(A) to 12(C) depict a third specific embodiment involvingpolymerization of a portion of the co-extruded primary and secondarymaterials to form a polymer structure that serves as the desired rigidpipe body. FIG. 12(A) depicts the co-extrusion of a primary material 56Cand a secondary material 57C using any of the techniques described aboveto produce a preliminary composite structure 110C-1 including sideportions 111C-1 and 112C-1, a central bead 114C disposed therebetween,and an upper portion 113C-1 that extends over central bead 114C. In thisembodiment primary material 56C includes both a catalyst and a monomer,and FIG. 12(B) depicts a subsequent polymerization process that causesat least a portions of the primary material forming side portions 111C-1and 112C-1 and upper portion 113C-1 to generate a polymer structure(pipe body) 110C-2 that surrounds central bead 114C. In one specificembodiment the catalyst comprises an ultraviolet (UV) reactive material,and activating the catalyst comprises illuminating the primary materialwith UV light, as indicated in FIG. 12(B). In another specificembodiment the catalyst and polymer are selected such that thepolymerizing reaction just requires thermal heat, and in this case thecatalyst is supplied to the co-extrusion printhead through a thirdinlet, and the printhead is modified to combine (mix) the catalyst withthe primary material/monomer immediately before leaving the orifice(e.g., in the merge point). FIG. 12(C) depicts pipe structure 110C-2after subsequent removal of any remaining non-polymerized primarymaterial and secondary material, whereby a central channel 115C-2 isformed that is defined by inside surfaces of side walls 111C-2 and112C-2 and upper wall 113C-2 of polymer structure (pipe body) 110C-2,and by surface portion 102-2. An advantage of this third approach isthat the primary and secondary materials can be co-extruded (printed) atroom temperature, and then solidified to form the solid walls.

FIGS. 13(A) and 13(B) depict a fourth specific embodiment involvingpolymerization that occurs at an interface between the co-extrudedprimary and secondary materials to form a polymer structure that servesas the desired rigid pipe body. FIG. 13(A) depicts the co-extrusion of aprimary material 56D and a secondary material 57D using any of thetechniques described above to produce a preliminary composite structure110D-1 including side portions 111D-1 and 112D-1, a central bead 114Ddisposed therebetween, and an upper portion 113D-1 that extends overcentral bead 114D. In this embodiment primary material 56D includes acatalyst and secondary material 57D includes a monomer (or vice versa)such that a polymerization process occurs at an interface of theco-extruded materials, whereby portions of the primary and secondarymaterials generate a polymer structure (pipe body) 110D-2 that surroundscentral bead 114D. FIG. 13( b) depicts pipe structure 110D-2 aftersubsequent removal of any remaining unpolymerized primary material andsecondary material, whereby a central channel 115D-2 is formed that isdefined by inside surfaces of side walls 111D-2 and 112D-2 and an upperwall 113D-2 of polymer structure (pipe body) 110D-2, and by surfaceportion 102-2. Advantages of this fourth approach are potentially lowermaterial costs than the other embodiments, and, because polymerizationoccurs only at the interface between the primary and secondarymaterials, the resulting polymer walls may be thinner than in the otherpolymerizing approaches, thus providing improved heat transfer throughthe polymer walls.

FIGS. 14(A) to 14(C) depict a fifth specific embodiment in which aprimary material 56E and a secondary material 57E are co-extruded orformulated in a way that promotes the flow of primary fluid 56E over theupper surface of a central bead 114E during or after the co-extrusionprocess. In one alternative of this embodiment, the interior channels ofthe printhead are manufactured in such a way that contact betweenprimary material 56E and the top of the channel is more energeticallyfavorable than contact between secondary fluid 57E and the top of thechannel. Given the layer-by-layer construction of the printhead, thisobjective could be achieved either through materials selection of thelayer that defines the top of the channel, or by specially treating thesurface of that layer. Given a long enough fluid path, the co-flowingstreams should reorient themselves to reduce total surface energy, withprimary fluid 56E surrounding secondary fluid 57E on three sides. Anadvantage of this fifth approach is that materials are extrudedside-by-side, allowing a simpler printhead, while still requiring asingle extrusion step.

FIGS. 15(A) to 15(C) depict a sixth specific embodiment in which aprimary material 56F and a secondary material 57F are co-extruded and/orsubsequently treated in a way that promotes “slumping” of primary fluid56F from side portions 111F-1 and 112F-1 over the upper surface of acentral bead 114F after the co-extrusion process. In this embodiment theshape of the extrusion nozzles are formed such that uppermost portions111F-11 and 112F-11 of side portions 111F-1 and 112F-1 extend higherabove the substrate than the upper surface of central bead 114F, asindicated in FIG. 15(A). Alternatively, the two materials can beextruded to form structures having the same height, but with the fluidproperties selected such that, upon cooling or drying, the volume ofsecondary material 57F reduces more rapidly than that of primarymaterial 56F. In this way, as indicated in FIG. 15(B), side portions111F-1 and 112F-1 collapse or “slump” to meet at a seam S above centralbead 114F, thereby forming an upper portion 113F-1 that seals thechannel region containing central bead 114F. FIG. 15(C) depicts pipestructure 110F-2 after subsequent curing/hardening of the primarymaterial portions and removal of the secondary material, whereby acentral channel 115F-2 is formed that is defined by inside surfaces ofside walls 111F-2 and 112F-2 and upper wall 113F-2 of the resulting pipebody 110F-2. An advantage of this sixth approach is that materials areextruded side-by-side, allowing a simpler printhead, while stillrequiring a single extrusion step.

Each of the above specific embodiments includes removal of the secondaryfluid (central bead) from the central channel in order to complete theformation of the desired pipe body structure. Removal of the secondarymaterial can be performed by one of several possible methods, includingtwo methods described below with reference to FIGS. 16(A), 16(B) and 17.The methods described below are intended to be illustrative of thepresently preferred approaches, and not intended to be comprehensive.

FIGS. 16(A) and 16(B) are simplified cross-sectional side views showingan elongated composite structure 110-1 formed in accordance with any ofthe embodiments set forth above, and in particular shows central bead114 and upper portion 113-1 disposed on substrate 101. In this specificembodiment, the secondary material forming central bead 114 maintains aliquid form during co-extrusion and the subsequent primary materialhardening process (e.g., curing by way of the application of heat, asindicated in FIG. 16(A). As indicated in FIG. 16(B), once the primarymaterial hardens (e.g., upper portion 113-1 becomes upper wall 113-2 inthe manner described above), removal of the secondary material (bead114) is performed by pumping the liquid out of the elongated centralregion using either pressurized gas P or a vacuum V (or both) to createa pressure differential between end openings 116-2 and 117-2. In anotherspecific embodiment, the secondary material can be designed to have alower melting temperature than the primary material, and the removalprocess involves heating composite structure 110-1 to temperature abovea melting point of central bead 114 and below a melting point of thepipe structure (e.g., upper portion 113-1) as indicated in FIG. 16(A),and then removing the melted secondary material from the elongatedcentral region/channel 115 of hardened pipe body 110-2 by pumping (e.g.,as shown in FIG. 16(B)).

FIG. 17 is are simplified cross-sectional side views showing a hardenedpipe body 110-2 formed in accordance with any of the embodiments setforth above. In this specific embodiment, the secondary material formingcentral bead 114 is removed by applying a selective etchant 400 thatdissolves the secondary material forming central bead 114, but does notdissolve the primary material forming, e.g., upper wall 113-2.

As set forth above, after the desired pipe body structure is formedusing any of the above specific embodiments and the secondary materialis removed, “charging” of the microchannel heat pipe is then performedby disposing a working fluid inside the elongated central channel, andthen the elongated central channel is sealed. Charging and sealing canbe performed by one of several possible methods, including two methodsdescribed below with reference to FIGS. 18(A) to 18(C) and 19(A) to19(C). The methods described below are intended to be illustrative ofthe presently preferred approaches, and not intended to becomprehensive.

FIGS. 18(A) to 18(C) are simplified cross-sectional side views showing apipe body 110-2 formed on a substrate 101 in accordance with any of theembodiments set forth above. FIG. 18(A) shows pipe body 110-2 andsubstrate 101 positioned such that end opening 117-2 is disposed in apool 510 containing a working fluid, with an optional vacuum V (or otherlow pressure) present at end opening 116-2, whereby working fluid 130 isdrawn into elongated central chamber 115 from pool 510 through endopening 117-2 by way of capillary action, displacing the air present inelongated central chamber 115. As indicated in FIG. 18(B), onceelongated central chamber 115 is filled with working fluid 130, one endof pipe body 110-2 (e.g., end opening 116-2) is sealed by way of a firstsealing structure (e.g., sealing structure 140-1), and then an amount ofthe working fluid inside elongated central chamber 115 is allowed toevaporate until the desired amount remains, at which time the second end(e.g., end opening 117-2) is sealed (e.g., by way of sealing structure140-2), thereby completing microchannel heat pipe 100.

FIGS. 19(A) to 19(C) are simplified cross-sectional side views showingcharging and sealing of pipe body 110-2 according to an alternativeapproach. FIG. 19(A) shows pipe body 110-2 and substrate 101 positionedsuch that end opening 117-2 is disposed in pool 510, as in the previousembodiment. However, in this case end opening 116-2 has already beensealed by way of sealing structure 140-1, and pipe body 110-2 has beenplaced in a pressure chamber set such that a vacuum V (or other lowpressure) is present in central chamber 115. This arrangement (which canbe enhanced, for example, by allowing the chamber pressure P toincrease) causes working fluid 130 to draw into elongated centralchamber 115 from pool 510 through end opening 117-2 by way of capillaryaction. As indicated in FIG. 19(B), once elongated central chamber 115is filled with working fluid 130, an amount of the working fluid insideelongated central chamber 115 is allowed to evaporate through endopening 117-2 until the desired amount remains, at which time the secondend (e.g., end opening 117-2) is sealed (e.g., by way of sealingstructure 140-2), thereby completing microchannel heat pipe 100.

In a third method, which is presently preferred, the heat pipe is placedin a pressure chamber filled with a dry gas, such as nitrogen. One endof the heat pipe is placed in a pool of the working fluid, similar tothe approach shown in FIG. 18(A) so that the fluid is drawn into theheat pipe via capillary action, or the working fluid is injected intothe heat pipe. When the desired amount of fluid is in the pipe, bothends are sealed.

Although the present invention has been described with respect tocertain specific embodiments, it will be clear to those skilled in theart that the inventive features of the present invention are applicableto other embodiments as well, all of which are intended to fall withinthe scope of the present invention. For example, although the presentinvention is described with reference to the use of micro extrusionprintheads that form high-aspect ratio central beads, other co-extrusionprintheads may also be used that do not form the secondary (sacrificial)material as a high aspect ratio bead. Further, elongated pipe bodystructures having cross-sectional shapes other than the substantiallysemi-circular (e.g., FIG. 1) and substantially square/rectangular (e.g.,see FIG. 11(B)) may also be formed using the methods described above,including that of pipe body 110G shown in FIG. 20(A) (i.e., where sidewalls 111G and 112G and upper wall 113G of pipe body 110G form apseudo-trapezoidal shape) or that of pipe body 110H shown in FIG. 20(B)(i.e., where side walls 111H and 112H and upper wall 113H of pipe-body110H form a pseudo-triangular shape).

1. A microchannel heat pipe disposed on a substrate, the microchannelheat pipe comprising: an elongated pipe body including first and secondelongated side wall portions that are disposed on a surface of thesubstrate and separated by an elongated central channel, and an upperwall portion extending between said first and second elongated side wallportions over the elongated central channel, whereby the elongatedcentral channel is defined by the first and second elongated side wallportions, the upper wall portion and a portion of the substrate surfaceextending between said first and second elongated side portions; and aworking fluid encapsulated inside the elongated central channel, whereinthe first and second elongated side wall portions and the upper wallportion comprise an integral structure consisting of a common material.2. The microchannel heat pipe of claim 1, wherein the elongated pipebody has a nominal width in the range of 10 micrometers to 500micrometers, a length in the range of 100 micrometers to 20 centimeters,and a nominal height in the range of 25 micrometers to 500 micrometers.3. The microchannel heat pipe of claim 2, wherein the elongated pipebody has a nominal width in the range of 30 micrometers to 200micrometers, a length in the range of 10 to 100 millimeters, and anominal height in the range of 30 micrometers to 200 micrometers.
 4. Themicrochannel heat pipe of claim 1, wherein the first and secondelongated side wall portions and the upper wall portion comprise across-sectional shape that is one of substantially semi-circular,substantially square, substantially rectangular, pseudo-trapezoidal andpseudo-triangular.
 5. The microchannel heat pipe of claim 1, wherein thecommon material comprises at least one of silver, copper, nickel, tin,aluminum, steel, alumina, silicates, glasses, carbon black, polymers andwax.
 6. The microchannel heat pipe of claim 1, wherein the first andsecond elongated side wall portions and the upper wall portion comprisea sintered metal.
 7. The microchannel heat pipe of claim 1, wherein thefirst and second elongated side wall portions and the upper wall portioncomprise a polymer.
 8. The microchannel heat pipe of claim 1, whereinthe working fluid comprises one of methanol, ethanol, water, acetone,and ammonia.
 9. The microchannel heat pipe of claim 1, furthercomprising first and second sealing structures respectively disposedover opposing end openings defined in the pipe body that communicatewith the elongated central channel.
 10. The microchannel heat pipe ofclaim 9, wherein the first and second sealing structures respectivelycomprise one of epoxy, silicone and solder.
 11. A microchannel heat pipedisposed on a substrate, the microchannel heat pipe comprising: anelongated pipe body including first and second elongated side wallportions that are disposed on a surface of the substrate and separatedby an elongated central channel, and an upper wall portion extendingbetween said first and second elongated side wall portions over theelongated central channel, whereby the elongated central channel isdefined by the first and second elongated side wall portions, the upperwall portion and a portion of the substrate surface extending betweensaid first and second elongated side portions; and a working fluidencapsulated inside the elongated central channel, wherein the first andsecond elongated side wall portions and the upper wall portion comprisea polymer structure.
 12. The microchannel heat pipe of claim 11, whereinthe elongated pipe body has a nominal width in the range of 10micrometers to 500 micrometers, a length in the range of 100 micrometersto 20 centimeters, and a nominal height in the range of 25 micrometersto 500 micrometers.
 13. The microchannel heat pipe of claim 12, whereinthe elongated pipe body has a nominal width in the range of 30micrometers to 200 micrometers, a length in the range of 10 to 100millimeters, and a nominal height in the range of 30 micrometers to 200micrometers.
 14. The microchannel heat pipe of claim 11, wherein thefirst and second elongated side wall portions and the upper wall portioncomprise a cross-sectional shape that is one of substantiallysemi-circular, substantially square, substantially rectangular,pseudo-trapezoidal and pseudo-triangular.
 15. The microchannel heat pipeof claim 11, wherein the working fluid comprises one of methanol,ethanol, water, acetone, and ammonia.
 16. The microchannel heat pipe ofclaim 11, further comprising first and second sealing structuresrespectively disposed over opposing ends of elongated central channel.17. The microchannel heat pipe of claim 16, wherein the first and secondsealing structures respectively comprise one of epoxy, silicone andsolder.
 18. A device comprising: a substrate having an upper surface; aheat generating region formed in the substrate; and a microchannel heatpipe disposed on the substrate, the microchannel heat pipe including: anelongated pipe body including first and second elongated side wallportions that are disposed on a surface of the substrate and separatedby an elongated central channel, and an upper wall portion extendingbetween said first and second elongated side wall portions over theelongated central channel, whereby the elongated central channel isdefined by the first and second elongated side wall portions, the upperwall portion and a portion of the substrate surface extending betweensaid first and second elongated side portions; and a working fluidencapsulated inside the elongated central channel, wherein the elongatedpipe body is disposed on the substrate such that the heat generatingregion is disposed under a first end of the microchannel heat pipe, anda second end of the microchannel heat pipe is disposed adjacent to aheat sink region of the device that is spaced from the heat generatingregion.
 19. The device of claim 18, wherein the device comprises anintegrated circuit including a central active region formed in thesubstrate under the first end of the microchannel heat pipe, and aperipheral inactive region disposed on the substrate and located underthe second end of the microchannel heat pipe.
 20. The device of claim18, wherein the first and second elongated side wall portions and theupper wall portion comprise an integral structure consisting of a commonmaterial.